Manufacture of non-woven fibrous webs

ABSTRACT

A process for making a substantially uniform web comprising traversing fiber or filament depositing means across a moving conveyor under conditions defined by the formula y 2x (t+z) where y is the total effective width of web deposited by the fiber or filament depositing means measured in the direction of travel of the conveyor, x is the speed of the conveyor, t is the turn round time of the fiber or filament depositing means, x is the traverse time of the fiber or filament depositing means and n is any whole number.

0 limited States 1 Patent 1151 3,669,868 Weightman 1 1 May 9, 1972 [54]MANUFACTURE OF NON-WOVEN [56] References Cited FIBROUS WEBS UNITEDSTATES PATENTS 3,183 557 5/1965 Hollowell ..l9/163 W t l, I [72] gm En3,222,730 12/1965 Kalwaites 19/163 3,394,435 7/1968 Knee v ..19/156.3[73] Assignee: Imperial Chemical Industri Limit ,460,731 8/1969Tr0th,1r. ..19/ 156.3 UX

London England Primary E.\'ar ninerDorsey Newton [22] Filed May 19 1969Attorney-Cushman, Darby & Cushman [21] Appl. No.: 325,841 [57] ABSTRACTA process for making a substantially uniform web comprising [30] ForeignApplication Priority D traversing fiber or filament depositing meansacross a moving M 29 1968 G tB "25 7 conveyor under conditions definedby the formula 2.\' 4 1968 ig; 2;}: ggigg (t+z) where y is the totaleffective width of web deposited by the fiber or filament depositingmeans measured in the [52] US. Cl ..l9/l63 direction of travel of theconveyor x is the speed of the 51 Int. Cl. 1 ..D04h 11 04 veyor, I isthe turn round time of the r or filament deposit- {58] Field of Search..l9/l63, 155,156,156.3; means, is the traverse time 0f the fiberfilament depositing means and n is any whole number.

2 Claims, 8 Drawing Figures P ATENTEBW 9 I972 3,660,868

sum 2 BF 6 27 I nventor A ttorney MANUFACTURE F NON-WOVEN FIBROUS WEBSThe invention relates to methods of producing non-woven fibrous webs andin particular relates to methods of depositing fibers or filaments toform webs using a traversing technique.

Methods for forming fibrous webs by forwarding fibers or filaments froma supply source, for example a hopper of staple fibers, a creel ofbobbins or a filament spinning machine, and depositing them on a movingcollecting surface are well known, the methods generally involving theuse of rotating rolls or air streams to transport and deposit the fibersor filaments. Such transporting and depositing devices have mainly beenlocated in stationary positions opposite the moving collecting surface.ln order to obtain uniform webs having an overall width greater thanthat produced by a single depositing device, it has been necessary toarrange a numberof devices side-by-side, ensure each device deposits auniform and similar array of fibers and filaments, position each devicecarefully and make use of complicated jointing techniques to ensure thecorrect degree of overlap. Such precautions demand great care and skilland have not been wholly successful. Even in cases where it has provedpossible to deposit reasonably uniform webs in this way there stillremain serious disadvantages in that failure of the fiber or filamentsupply to one of the depositing devices will create an unacceptablediscontinuity along the length of the web and in that the webs producedby stationary depositing devices have little coherency and are difficultto handle without disturbing the fiber or filament distribution.

It has been proposed to overcome some of the aforesaid disadvantages bytraversing depositing means across the width of the moving collectingsurface. Such methods have hitherto proved unsatisfactory because of thedifficulty of choosing traverse operating conditions which give a web ofuniform weight per unit area, the methods generally producing areaswhere very few or no fibers or filaments have been deposited and otherareas where, for instance, double thicknesses have been deposited.

We have now discovered a method of operating a depositing means traversesystem which will produce a web of uniform weight per unit area andaccordingly the present invention, in one of its aspects, comprises amethod of forming a fibrous web on an advancing collecting surface whichcomprises traversing fiber or filament depositing means in areciprocating manner across a collecting surface in directionstransverse to the direction of movement of said collecting surface sothat y 2m (1 z) where Y is the total effective widthof web deposited bythe depositing means measured in the direction of travel of thecollecting means, is the speed of the collecting surface, I is theturn-around time of the depositing means, 1 is the traverse time of thedepositing means and n is any positive integer. The turn round time, t,may be constant or it may be a function of traverse time, z, dependingon the design of the traverse mechanism.

The depositing devices may be traversed across the collecting surface byfor instance mechanical, pneumatic or hydraulic means or by means of alinear induction motor, and the fact that any such traversing meanstakes a finite time to reverse its direction is one of the reasons forthe inclusion of the term tin the formula relating to the method of thepresent invention. Thus the turn-round time t is the time elapsing fromthe moment when the depositing devices start to decelerate havingtravelled across the width of the collecting means to the moment whenthe depositing devices cease to accelerate when travelling in theopposite direction. The depositing devices may continue to functionduring the turn round time but the web will be non-uniform and may beconveniently removed by edge trimming. The only limitation concerningthe type of traverse used is that it should travel substantiallyuniformly across the collecting surface.

In the most simple case in which a single depositing device is used, yis taken as the effective width of the web deposited by that devicemeasured in the direction of travel of the collecting means. Thiseffective width is dependent on the total width of web produced by thedevice and the distribution of fibers or filamentsin the web, which inturn depend on the type and design of the depositing device. lf thedistribution is substantially uniform then the effective width is equalto the total width but if the distribution is non-uniform then theeffective width is equal to some function of the total width dependingupon the actual shape of the distribution.

The depositing devices may be pairs of nip rolls or baffle plates whichgenerally produce an approximately rectangular distribution. We havefound, especially when depositing continuous filaments, that airejectors are most useful. Such air ejectors, depending upon theirdesign, may, when stationary, deposit circular, elliptical orrectangular shaped webs and for each type of ejector it is necessary todetermine the distribution of filaments in the webs produced and thenthe effective widths. Rectangular shaped webs produced from rectangularslot-type ejectors are normally substantially uniform across their widthand generally the effective width is substantially the same as the totalwidth. Circular and elliptical shaped webs however such as are producedfrom ejectors of say circular cross-section usually have a non-uniformdistribution of filaments across their widths. Such distributions oftenapproximate to Gaussian distributions and in this case the effectivewidth should be taken as the Half-Peak Width.

Once the effective width, y, of the single depositing device is found,the following procedure is adopted to calculate the conditions whichwill give a product having uniform thickness or weight per unit area.The throughput of fibers or filaments through the depositing device willbe known, as will the weight per unit area of product required. Thewidth of the product will also be known and depends on the length oftraverse of the depositing device. From these fixed parameters theconveyor speed, .r, is readily calculated. The values of y and .r aresubstituted in the equation representing the conditions for uniformweight per unit area, y 2xn (1+ 2) and the values of 2 (1+ z), thetraverse cycle time, are found for n l, 2, 3, etc.

For all integral values of n, a uniform product is obtained havingconstant weight per unit area, and the number of layers of web depositedat any position in the web will be given by 211. Thus if n I, all partsof the conveyor surface will be covered twice, and if n 3 all parts ofthe conveyor surface will be covered six times by an individual webhaving a weight per unit area equal to one third of that deposited whenn l.

The value of n may be chosen to give a pattern of covers most suited toa particular end-use, but frequently only a limited number of choices ofn will be available because of traverse machinery speed limitations.

Often, however, the use of a single depositing device is undesirable,because of the undesirably low collecting surface speeds, x, andthrouputs associated therewith and, in an attempt to increaseproductivity, undesirably high traverse speeds may result. A number ofdepositing devices can be used to increase throughput and preferablyeach individual depositing device gives a uniform cover by conforming tothe equation y Znx (t z). The use of more than one depositing deviceprovides an opportunity for conveyor speed to be increased. Theresulting web will be composed of a number of superimposed uniform webs.

If the effective widths, y, of the several depositing devices aresubstantially similar, the several depositing devices may convenientlybe attached to a single traversing device aligned in a directionparallel to the direction of motion of the collecting surface. Sinceeach device is individually producing uniform cover the spacing of thedevices along the traversing device is not important provided that thedepositing devices do not interfere with each other.

When the conveyor speed is increased as a result of provision of aplurality of depositing devices in order to increase the rate ofproduction of a web of desired weight, it frequently happens that thepreferred condition of operation, in which each depositing device givesuniform cover, is unattainable because of the excessively high traversespeeds required to satisfy the condition y 2m: (t'+ z). In such cases,it becomes necessary to group a number of depositing devices together insuch a manner that the group itself produces a uniform web by obeyingthe relationship Y= 2m (1 z), where Y is the effective width depositedby the group of depositing devices measured in the direction of advanceof the collecting means.

The devices are spaced apart within the group so that the totaleffective width Y of the group is the sum of the effective widths y y yetc. of the webs produced by each of the devices working in conjunction.

The individual depositing devices forming the group may be groupeddirectly adjacent to each other and traversed together at spacingdepending upon their effective widths y y y etc., or may be spaced apartalong the length of the collecting surface and traversed together oroppositely depending on their spacing. This latter spacing will again becritically dependant on the effective widths y y y etc., of the websproduced by the several depositing devices and will be such as toeventually build up a continuous total effective width Y.

The throughput of the process can be still further increased by having aplurality of groups of depositing devices, each group producing auniform web.

The invention therefore provides a means of producing a uniform web fromone or more individual depositing devices each giving individually auniform web by obeying the relationship y 211x (t z), or one or moregroups of depositing devices, each group individually giving a uniformweb by obeying the relationship Y= Znx (t z).

The arrangement of depositing devices is a matter of choice althoughwhere possible each device should preferably give uniform cover. In suchprocesses it is of course highly desirable that a uniform product beobtained at all times, including during involuntary failure of one ormore of the depositing devices. The means of achieving such a uniformityof product during involuntary failures of a number of depositing devicesis an important aspect of the invention, and is now described.

In all cases, the involuntary failure of a number of depositing deviceswill result in a reduction in the overall weight per unit area of theweb. In order to restore the web to its former weight per unit area itis necessary to reduce the speed of the collecting surface, x, to a newvalue x*. However, in the majority of cases the change ofx to willresult in uniformity of product being lost, since the new relationship y2nx* (t z) in which n is an integer, will only rarely be satisfied. Itwill be seen therefore that it will also be necessary to change thevalues of effective width, y, or to change the traverse time and/or turnaround time (z +1), or a combination ofy and (z I), to re-establish anintegral value for n.

For example, suppose that there are q groups of depositing devices, eachgroup containing p depositing devices and each group individuallyproducing a uniform web and having an effective width, Y. Then eachgroup must be obeying the relationship y 2nx (I z). The conveyor speed,x, has been chosen to give a product having a desired weight per unitarea with all q-p depositing devices functioning. Now supposing that inone group, 5 depositing devices fail. Since it is the group as a wholewhich produces a uniform cover it will be necessary to deliberately failthe remaining (p 5) devices in that group in order to be able to regainthe uniform product. Hence on failure of any 5 devices in a group, thenumber of devices lost due to inadvertant and deliberate failure will bep. If the 5 devices are not all in the same group it will be necessaryto fail rp. devices where r is the number ofgroups affected.

Now for a given weight per unit area the speed of the collecting surfaceis proportional to the number of devices. Therefore, we have Beforefailure: xa-pq After failure: xa(pqpr) Thus in order to re-establish theformer weight per unit area it is necessary to reduce the conveyor speedby x(r/q) where r is the number of groups failed and q is the totalnumber of groups.

In order to re-establish uniformity the equation Y 2n.\"' (I 1) must besatisfied. Hence the value Y or (t z) or a combination thereof must bechanged to restore an integral value to n. It may occasionally happenthat n has an integral value after alteration of.\' to the conditionbeing that q/tq-r). n is an integer. However in the vast majority ofcases it is necessary to alter the effective width, Yor the traverseand/or a turn round time (1 t). It is impractible to alter the effectivewidth. Y since this depends on design and type of depositing device andupon the number of devices in the group. Accordingly in practical casesit is (z t) which is altered and this is considered below.

Let it be necessary to alter (z +1) to T in order to satisfy therelationship Y= 2n*x*7" where n is an integer but In all cases it willbe found that n n* or n* can be made to equal n. So

The value of (z t) can be altered by altering (i) the traverse time, z,(ii) the turn round time, t and (iii) both traverse time and turn roundtime. In case (i) z is altered to z* and in case (iii). (2+!) is alteredto (z+l)* Should it be desired to retain the term, (2 +1), at a constantvalue, then it is necessary, in addition to reducing the con- VeyOIspeed to to reduce the effective width to to maintain uniformity of webweight per unit area.

By such a procedure, a web of uniform density is maintained, although ofcourse the structure and number of overlaid laps are altered.

It is therefore necessary to deliberately fail a number of depositingdevices so that remaining groups each give uniform cover and to adjustconveyor speed, and traverse time or effective width to maintainproduction of a uniform web, as described above. However, if a minimumweight of web only is required and the number of failed depositingdevices is small compared with the total number of depositing devices,then the remaining depositing devices might conveniently be permitted tocontinue functioning to produce a web with slightly varying weight alongits length. I

The above procedure is also applied in the case of inadvertant failureof depositing devices, each of which individually produces a uniformweb. This case is a specific example of that described above, in whichthe number of depositing devices in a group giving a uniform web is one.Hence there is no necessity to fail deliberately any depositing devices.

The method of production of a uniform web before and after failure of anumber of depositing devices may conveniently be automated by use offailure detecting devices and automatic switching to change thecollecting speed, x, and the speed of traverse of the depositing devicesin a conventional manner.

The value of n chosen will depend upon the weight required for the finalweb, the coherency desired in the final web, magnitude desired for thethroughput from each depositing device, the traverse speed and theconveyor speed and is generally chosen to give the best compromisebetween these factors.

The collecting surface itself may conveniently be a foraminous conveyorbelt but the actual nature of the belt will depend on the nature of thedepositing devices used and may be a drum or flat imperforated surface.

The invention will now be described in more detail with reference to theaccompanying drawings of which:

FIG. 1 shows an end view of a continuous filament web depositingapparatus;

FIG. 2 shows a section taken along the line A A ofFIG. 1;

FIGS. 3 6 show diagrammatically the construction of webs formed by asingle fiber or filament depositing device giving uniform cover indifferent modes of operation according to the invention;

FIG. 7 shows diagrammatically the construction of a web formed by twofiber or filament depositing devices having differing effective widthsacting in conjunction to produce a uniform web;

FIG. 8 shows diagrammatically the construction of a nonuniform webproduced by the failure of one of the depositing devices used to producethe web ofFIG. 7.

Referring to the drawings in more detail, FIGS. 1 and 2 show views ofapparatus in which two rectangular air ejectors are traversed together.The apparatus consists of a pair of forwarding rolls 10 mounted intandem and a pair of smaller rolls 11 forming nips with the rolls 10,two air ejectors 12 spaced apart a specified distance affixed to amounting block 13 by angle iron 14 and having mounted thereon bandingdevices 15, a runner bar 16, along which the mounting block 13 slides,supported by frameworks 17 and 18, a driving chain 19 affixed to themounting block 13 and supported at its ends by sprocket means (notshown) mounted in frameworks 17 and 18, the sprocket means being drivenvia electromagnetic clutches by driving motors (not shown) mounted inframeworks 17 and 18 so that the mounting block 13 is traversed back andforth along the runner bar 16, and a foraminous conveyor belt 20situated between frameworks 17 and 18 so that it travels in a directionat right angles to that of the mounting block. The ejectors 12 are fedwith high pressure air via pipes 21, connected through valves 22 mountedon block 13 to extensible hose 23.

In practice two continuous filament threadlines 24, taken from aspinning head (not shown), pass around the forwarding rolls 10 throughthe nips formed by rolls 10 and 11 and are entrained into air ejectors12 via banding devices 15. The air ejectors 12 deposit the continuousfilaments on the conveyor belt 20 in the form of webs 25 which justoverlap to form a continuous uniform width equal to the total effectivewidth of web as hereinbefore defined. The conveyor speed, the

traverse time and the turn round time are adjusted in accordance withthe formula y 2m (1 z) and the apparatus run to produce a uniformcontinuous filament web. The apparatus may include a plurality ofdepositing means disposed along the length of conveyor belt 20 asillustrated in FIG. 2 wherein primed reference numerals designate asecond group of depositing elements.

FIGS. 3 to 6 show diagrammatic plan view of webs formed by a singlefiber or filament depositing device giving uniform cover in differentmodes of operation according to the invention. FIG. 3 shows the patternof web produced with n l, and FIGS. 4, 5 and 6 show the patterns with n2, 3 and 4 respectively. In all of these figures the effective width ofweb deposited is the same and is indicated by the distance betweenpoints 26 and 27. Points 28 and 29 indicate the position of webdeposition after a single traverse of the depositing device across thecollecting surface from the position indicated by points 26 and 27,assuming that the collecting surface is moving from right to left in thefigures. The effect of a finite turn round time for the traversingdepositing devices is shown by the gap between points 30 and 31 on theweb.

Lines 32 in FIGS. 3 6 indicate widths of web deposited in any traverseand the number of lines 32 crossing any particular portion of the webindicates the number of covers constituting that portion of the web. Itis seen that between initial and final traverses the webs produced areuniform, having a number of covers equal to Zn. Other depositing devicesmay be used also operating in according to the invention to superimposetheir uniform webs on the uniform base web and may be spaced at anypoints above the collecting surface.

FIG. 7 shows a diagrammatic plan view of a web produced by twodepositing devices, one having an effective width equal to twice theother, co-operating to produce a uniform web. For convenience the effectof a finite turn round time has been ignored. Points 36 and 37 indicatethe effective width of web deposited by one depositing device and points38 and 39 indicate the effective width deposited by the second device.The devices are so positioned that they produce a combined effectivewidth equal to the distance between points 36 and 40.

The devices may be traversed together and arranged sideby-side so thatthey deposit webs between points 36 and 37 and 37 and 40, may betraversed together and spaced apart defined distances so that, forinstance, one device deposits web between points 36 and 37 and the otherdevice deposits web between points 38 and 39 or may be traversedoppositely to one another so that, for instance, one device deposits webbetween points 36 and 37 and the other device deposits web betweenpoints 43 and 44 or, say,4l and 42.

FIG. 8 shows the web produced by the depositing devices employed tomanufacture the uniform web of FIG. 7 with the device having the smallereffective width failed. The resulting web is non-uniform having areas45, 46, 47 in which there is double cover, areas 48, 49, 50 in whichthere is single cover and uncovered areas 51, 52 and 53.

The invention will be further described by the following Example.

EXAMPLE Eight air ejector depositing devices having substantiallysimilar effective widths were attached to a common mounting which wastraversed above an endless conveyor advancing perpendicularly to thedirection of traverse of the depositing devices. The air ejectors werefound to give an elliptical distribution of deposited filaments and theeffective width of the devices was found to be 25 29 cm. The conveyorwas arranged to advance 27 cm. in each complete traverse cycle.Continuous filaments of polyhexamethylene adipamide were fed to all ofthe devices and the throughput was such that a product having a nominalweight of 6 oz./yd. (about 210 g.m. was obtained. Each device thusobeyed the relationship y 2x (t z), i.e. gave individually substantiallyuniform cover as shown diagrammatically in FIG. 3 of the accompanyingdrawings.

Samples of the web measuring 20 X 20 cm. were cut at intervals from theweb and their weights measured. The mean weight of twelve 400 cm.samples was 8.27 g. and the standard deviation was 0.44.

Further samples measuring 100 X 5 cm. were taken across the web and themean weight of twelve samples was found to be 10.25 g. The standarddeviation was 0.44.

The value of standard deviation was due to the varying effective widthsof the depositing devices. When two devices having the same effectivewidth of 27 cm. were used to make a nominal 6 oz./yd. (2l0 g./m. web themean weight of 12 samples measuring 20 X 20 cm. was found to be 8.15 g.and the standard deviation was 0.08.

What 1 claim is:

1. A method of forming a fibrous web having at least a substantiallyuniform weight per unit area which comprises traversing a plurality ofdepositing devices in a reciprocating manner above a continuouslyadvancing collecting means in directions perpendicular to the directionof advance of said collecting means and depositing thereon a web offibers or filaments such that y 2nx (t z) where y is the effective width(as herein before defined) of said web deposited by said depositingmeans measured in the direction of travel of said collecting means; atis the speed at which said collecting means advances; z is the traversetime of said depositing means; t is the turn around time of saiddepositing means and n is any positive integer and further includingreducing said speed of said collecting means, .r,on failure of one ormore said depositing devices by the fraction obtained by dividing thenumber of said failed depositing devices by the total number of saiddevices and simultaneously increasing the total traverse cycle time bythe reciprocal of the said fraction.

2. A method of forming fibrous webs having an at least substantiallyuniform weight per unit area which comprises traversing a plurality ofgroups of depositing devices in a reciprocating manner above acontinuously advancing collecting means in a direction perpendicular tothe direction of advance of said collecting means and depositing thereona web of fibers or filaments such that y 2nx (z t) where y is theeffective width (as hereinbefore defined) of said web deposited by saiddepositing means measured in the direction of travel of said collectingmeans; x is the speed at which said collecting means advances; z is thetraverse time of said depositing means; I is the turn around time ofsaid depositing -means and n is any positive integer formed and saidindividual depositing devices are so arranged within said groups thatthe individual webs produced by said individual depositing devicescombine with webs formed by other depositing devices within a group toform a uniform web such that Y= 2nx (I z) where Y is the effective width(as hereinbefore defined) of said web deposited by the depositingdevices within a single group measured in the direction of travel ofsaid collecting means; x is the speed at which said collecting meansadvances; z is the traverse time of said depositing means; I is the turnaround time of said depositing means and n is any positive integer andfurther comprising that upon on failure of one or more devices in onegroup or more groups of devices, the remaining devices functioning ineach affected group of devices are deliberately deactivated and thespeed of said collecting surface is reduced by the fraction obtained bydividing the number of failed groups of devices by the total number ofgroups and simultaneously increasing the total traverse cycle time bythe reciprocal ofthe said fraction.

1. A method of forming a fibrous web having at least a substantiallyuniform weight per unit area which comprises traversing a plurality ofdepositing devices in a reciprocating manner above a continuouslyadvancing collecting means in directions perpendicular to the directionof advance of said collecting means and depositing thereon a web offibers or filaments such that y 2nx (t + z) where y is the effectivewidth (as herein before defined) of said web deposited by saiddepositing means measured in the direction of travel of said collectingmeans; x is the speed at which said collecting means advances; z is thetraverse time of said depositing means; t is the turn around time ofsaid depositing means and n is any positive integer and furtherincluding reducing said speed of said collecting means, x,on failure ofone or more said depositing devices by the fraction obtained by dividingthe number of said failed depositing devices by the total number of saiddevices and simultaneously increasing the total traverse cycle time bythe reciprocal of the said fraction.
 2. A method of forming fibrous webshaving an at least substantially uniform weight per unit area whichcomprises traversing a plurality of groups of depositing devices in areciprocating manner above a continuously advancing collecting means ina direction perpendicular to the direction of advance of said collectingmeans and depositing thereon a web of fibers or filaments such that y2nx (z + t) where y is the effective width (as hereinbefore defined) ofsaid web deposited by said depositing means measured in the direction oftravel of said collecting means; x is the speed at which said collectingmeans advances; z is the traverse time of said depositing means; t isthe turn around time of said depositing means and n is any positiveinteger formed and said individual depositing devices are so arrangedwithin said groups that the individual webs produced by said individualdepositing devices combine with webs formed by other depositing deviceswithin a group to form a uniform web such that Y 2nx (t + z) where Y isthe effective width (as hereinbefore defined) of said web deposited bythe depositing devices within a single group measured in the directionof travel of said collecting means; x is the speed at which saidcollecting means advances; z is the traverse time of said depositingmeans; t is the turn around time of said depositing means and n is anypositive integer and further comprising that upon on failure of one ormore devices in one group or more groups of devices, the remainingdevices functioning in each affected group of devices are deliberatelydeactivated and the speed of said collecting surface is reduced by thefraction obtained by dividing the number of failed groups of devices bythe total number of groups and simultaneously increasing the totaltraverse cycle time by the reciprocal of the said fraction.